I860.] 



THE SOUTHERN PLANTER. 



391 



their own elements, play a peculiar part, 

 which may he compared to the digesting ac- 

 tion of the stomach, and in which they can 

 partly replace each other ; and inasmuch 

 then as they prepare the food existing in the 

 soil for the process of nutrition, and render 

 it more fit for assimilation, they must neces- 

 sarily exert a powerful influence on the 

 growth of plants. 



We can now understand why these salts 

 exercise a favourable action in the cultiva- 

 tion only on certain soils, and w^hy on a 

 second or third application of them, the 

 same effect is only partially, or not at all re- 

 produced. 



An agriculturist in possession of fields con- 

 taining abundance of phosphates^ but une- 

 qually distributed through them, would, 

 were all other conditions the same, undoubt- 

 edly increase the activity of these phos- 

 phates, and thereby augment the produce of 

 his fields, if he possessed the means of with- 

 drawing the basic phosphates from the soil 

 and restoring them in the form of super- 

 phosphate. These means he actually em- 

 ploys, when he manures his fields with Chili 

 saltpetre, ammonia salts^ or chloride of so- 

 dium. 



For the Southern PI miter. 



Agricultural Geology. 



( Continued from the May number,^ 

 BY PROF. J. L. CAMPBELL. 



It has been already stated, that the strati- 

 fied rocks of the earth have been classified 

 by geologists into several distinct groups, 

 called " Formations." Of these we can give 

 but a brief and very general view. If the 

 reader could be favored with a view of the 

 neat lithographic cut, forming the frontis- 

 piece of the work on Agriculture, from 

 which the substance of this article is taken, 

 it would greatly aid the memory in retaining 

 a knowledge of the relative position, and of 



the names of the several formations. But, 



as the original figure is not within our reach 



at present, the ingenuity of the printer has 

 contrived the figure given below, which m 

 serve our present purposes as a temporar 

 substitute. It is designed to represent 

 ideal section the earth's crust, made at some 

 point where all the formations are found. 

 But the reader must beware of falling into 

 the mistake of supposing that each one of 

 these classes of rocks may be found every- 

 where, as a constituent of the earth's crust; 

 or that any one of them ever enveloped the 

 whole globe ) or that one of them cannot 

 occur without being accompanied by the 

 others ; or that, when found, they uniformly 

 all succeed each other in the order here 

 given. 



By examining the surface of the earth, as 

 represented by the top of the figure, it will 

 be seen that one formation alone may give 

 character to the rocks and soil for a distance 

 of many miles together, as in the space be- 

 tween a and 5, where the Tertiary formation 

 (8) crops out from beneath the Drift (9). 

 Again, the Primary Rocks (1), on the left 

 of the figure, may have been deposited over 

 a very wide section of ocean-bottom ; a por- 

 tion of them may have been subsequentl}'^ 

 elevated above the sea-level, and have again 

 subsided at the period wh^en the New-Red 

 Sandstone (5) was being deposited. A second 

 upheaval may have brought this formation 

 above the water, where it remained until the 

 Tertiary period (8) when sinking beneath 

 the ocean, it formed the bed upon which 

 this newest of the regularly stratified for- 

 mations was deposited. Thus rocks widely 

 separated in the regular series where all the 

 formations are represented, as on the right 

 side of the figure, are brought, under some 

 circumstances, into close poximity, as at c. 

 Taking the stratified rocks in their ascend- 

 ing order, we shall give the most prominent 

 characteristics of each formation. 



ch 

 las 



ir,' 



1, Primary Stratified Rock ; 2 

 5, New Red Sandstone ; 6, Ooliti 

 10, An Unslratified Mass of Igneous Rocli 



Silurian; 3, Old Red Sandstone; 4, Carboniferous or Coal 

 and Lias; 7, Cretaceous ; 8, Tertiary; 9, Alluvium and Drift; 



